Biosynthesis of cyanogenic glucosides in and the evolution of oxime-based defenses.

Lima bean, , is a crop legume that produces the cyanogenic glucosides linamarin and lotaustralin. In the legumes and , the biosynthesis of these two α-hydroxynitrile glucosides involves cytochrome P450 enzymes of the CYP79 and CYP736 families and a UDP-glucosyltransferase. Here, we identify CYP79D71 as the first enzyme of the pathway in , producing oximes from valine and isoleucine. A second CYP79 family member, CYP79D72, was shown to catalyze the formation of leucine-derived oximes, which act as volatile defense compounds in spp. The organization of the biosynthetic genes for cyanogenic glucosides in a gene cluster aided their identification in . In the available genome sequence of , the gene orthologous to is adjacent to a member of the family. Although is not cyanogenic, it does produce oximes as volatile defense compounds. We cloned the genes encoding two CYP83s (CYP83E46 and CYP83E47) and a UDP-glucosyltransferase (UGT85K31) from , and these genes combined form a complete biosynthetic pathway for linamarin and lotaustralin in Lima bean. Within the genus , the occurrence of linamarin and lotaustralin as functional chemical defense compounds appears restricted to species belonging to the closely related Polystachios and Lunatus groups. A preexisting ability to produce volatile oximes and nitriles likely facilitated evolution of cyanogenesis within the genus.